A processing apparatus, which performs plasma processing, is used to manufacture an electronic device such as a semiconductor device (see, for example, U.S. Pat. Nos. 6,468,816 and 6,244,121). The processing apparatus disclosed in U.S. Pat. Nos. 6,468,816 and 6,244,121 has a chamber and a placement table. The placement table is provided in the chamber and holds an object placed thereon. In the processing apparatus, the object is transported by a transport device and placed on the placement table, and the object is processed by plasma of a processing gas which is produced in the chamber. A transport device detects a transportation state by transporting a sensor device having the same shape as the object.